When I was @ Phantom Ranch last week with the GCHBA Volunteer project, one of the things we spoke with the rangers about was how they are gradually phasing out Cottonwood trees in the BA campground in favor of other riparian species (specifically Box Elder and Ash) because of the falling limb danger. I guess there's just too much liability associated with the possibility of crushed tourist. Of course, the struggle is that ashes grow much more slowly and are overall much smaller trees than cottonwoods, and the box elder's are struggling to survive at all on the high shelf above the creek (they're usually found right along the creek's margins with their feet right in the water). It's amazing how much work the expectation of dry, flood free, hazard free, shady camping has meant at BA. I'm amazed those permits don't cost more!
Personally, as a hammocker I find that paying attention to which trees are alive or dead is totally critical. Hanging from a dead tree =
Hanging from a healthy tree =